This invention relates to a powdered phenolic resin composition suitable for use in the dry process for the preparation of resin-bonded felt.
Resin-bonded felt is made by incorporating a thermosetting or thermoplastic resin into a fibrous bed followed by heating and/or curing the resin to hold the fibers in a compressed state to form a felt or felted material. The resin may be cured or semi-cured to form an intermediate or final product.
Felt, made by incorporating a thermosetting or a thermoplastic resin into a pad of carded fiber, is generally called resin-bonded felt. Resin-bonded felt relating to the present invention is ordinarily obtained either by curing or semi-curing a powder phenolic resin at a temperature range of 130.degree.-220.degree. C. subject to hot blowing air, after incorporating 10-30 parts by weight of said powder phenolic resin into 100 parts by weight of loose fiber with successive carding. The resin-bonded felt thus obtained is classified as cured felt and semi-cured felt. Cured felt is generally used as it is for cushioning, sound absorption or thermal insulation materials. As for semi-cured felt, the phenolic resin binder thereof remains still in an incomplete stage of curing, so it is further pressed under heat and formed to rigid articles used for structural parts of automobiles, such as ceiling cores or dashboard components.
A well-known exemplary manufacturing system of resin-bonded felt by incorporating a powder phenolic resin into fiber is disclosed in the Japanese Patent Publication No. Sho 44-4876. Generally, when phenolic resin is used as a binder of felt, owing to the comparatively weak cohesive strength of fiber, even a slight adhesion of the felt to the forming surfaces by said phenolic resin causes poor release of the felt after the heating step of manufacture.
Poor release results in a disfigured torn surface felt, which is unacceptable in market, being inferior in appearance, density and strength. On the other hand, due to energy-saving reasons, a phenolic resin having a rapid rate of cure is required for shortening the heating time during felt manufacture. Several methods are known for improving the rate of cure of novolac type phenolic resins: use of ortho-novolac type, incorporating an aromatic monocarboxylic acid such as salicyclic acid thereinto (Japanese Patent Application No. Sho 36-20589), incorporating a bivalent metal salt thereinto (Japanese Patent Application No. Sho 40-26719), etc.
After much investigation to improve the rate of cure of phenolic resins as well as to improve the release of the felt obtained from the conveyor-belt during the manufacture thereof, the inventors have found that a powder phenolic resin composition, comprising 0.3-5 parts by weight of an aromatic carboxylic acid to 100 parts by weight of the resin and the composition having a bulk density of 0.29-0.36 g/cm.sup.3, improves the rate of cure of the phenolic resin as well as release of the felt from the conveyor-belt.
Aromatic carboxylic acids according to the present invention have a formula of R--Ar--COOH, wherein;
R is selected from hydrogen, hydroxy group or alkoxy group, and PA1 Ar is selected from phenyl group, phenylalkenyl group or phenylalkyl group. PA1 R is selected from hydrogen, hydroxy or alkoxy groups, and PA1 Ar is selected from phenyl, phenylalkenyl or phenylalkyl groups.
It is an object of this invention to provide a phenolic resin composition for dry process felt production that will allow the release of the felt from the fiber retaining surfaces in a clean manner.
It is an additional object of this invention to provide a phenolic resin composition that will cure rapidly to allow greater speed of production.